Need to install old version of TimescaleDB that is supported with PG12

Hi all,

I need to install an older version of timescaledb as i need to migrate a pg12 database to something newer (current version of timesdcaledb in nixpkgs does not support pg12).

So the question is how do i pin postgresql12Packages.timescaledb to a git commit from last year?

Also as that references pg12 should it pin itself to the last supported version instead?